Principle of Unreasonableness in Administrative Law and its Reflection on the Jurisprudence of the Administrative Justice Court

In this article, we want to analyze the essence of the principle of unreasonableness as a judicial review ground in common law and its application in the jurisprudence of the Administrative Justice court. For this purpose, its concept, the twofold conception and categories of unreasonable decisions in UK case law are examined. Also, cases of Administrative Justice Court are expressed that could be construed in the light of unreasonableness. There are cases in jurisprudence of Administrative Justice Court that are included in expansive reading of unreasonableness for example reversal of principle of equality and non-discrimination, rationality and flaws in logic and reasoning, fair balance between relevant considerations, the failure of a public authority to have regard to a relevant consideration and taking into account of a legally irrelevant consideration, mistake of fact and oppressive decisions for example a gratuitous interference with the rights of the occupier and preventing to access to court.